The present invention relates to a novel cation-modified acrylamide or methacrylamide copolymer as well as to an antistatic agent, thermoplastic resin composition, aqueous composition and thermoplastic resin laminate comprising said cation-modified copolymer.
Cation-modified polyolefins retain the excellent processability, low temperature characteristics and flexibility of polyolefins and have cationic groups and, therefore, they are in wide use as antistatic agents, electroconductive resins, agents for statically charging toners, sizing agents for paper, antimicrobial agents, glass coating agents and so forth and are becoming industrially important materials.
Such cation-modified polyolefins include, for example, the following species (a) through (i):
(a) In EP-A-0258724 and JP-A-63057609, there are disclosed modified polyethylenes with a molecular weight of 500 to 10,000 (preferably 1,000 to 5,000) as derived from polyethylene by introducing 1 to 10 (preferably 1 to 5) cationized acrylamide units per molecule into polyethylene side chains. They are supposed to be useful as coating agents for glass vessels.
The method of production thereof, as disclosed, comprises reacting oxidized polyethylene with a molar excess of a dialkylaminoalkylamine for amidation, followed by quaternization with a quaternizing agent such as an alkyl halide or an alkyl sulfate ester.
(b) In JP-A-63246750, there are disclosed cation-modified polyolefins derived from a copolymer resin produced from an unsaturated carboxylic acid such as maleic anhydride or acrylic acid and an olefin by reacting the resin with at least 1 mole, per mole of the carboxyl group, of an amine such as N,N-dimethyl-1,3-propanediamine for conversion into an imide, amide or amine salt, followed by exhaustive or partial quaternization with a quaternizing agent such as an alkyl halide, aryl halide, trialkyl phosphonate or alkylaryl sulfonate, optionally further followed by modification of the negative counter ion structure by reaction with a sulfonic acid salt, for instance. It is disclosed that these cation-modified polyolefins are useful as agents for statically charging toners to be used in electrophotography.
(c) In JP-A-63304010 and JP-A-02036106, there is disclosed a method of preparing an aqueous dispersion of cation-modified polyethylene which comprises quaternizing, with an epihalohydrin, the hydrochloride of an ethylene-dialkylaminoalkylacrylamide or ethylene-dialkylaminoalkylacrylamide-methacrylate ester (the latter ester being introduced as a matter of convenience on the occasion of production and for the purpose of increasing the copolymer flexibility) copolymer obtained by radical copolymerization having a molecular weight of 5,000 to 50,000. The product thus obtained is allegedly effective as an antistatic agent to be applied to plastic films, as an electroconductive layer of a medium of electrostatic recording, and as a microbicide.
(d) In JP-A-04198308 and JP-A-04198307, there are disclosed, by the present inventors, ethylene-acrylate ester-acryloylaminoalkyltrialkylammonium copolymers and a method for their production. The cation-modified copolymers contain acrylic acid ester units positively introduced thereinto and, as a result, have the following practical advantages.
Thus, when incorporated into thermoplastic resins, they provide the resins with toughness and shock resistance, hence causing only slight decreases in physical characteristics. When used in the conductive layer of an electrostatic recording medium, they show good film-forming property and bring about good conductivity as well as good solvent resistance. Furthermore, when used, in an aqueous dispersion form, as coating-type antistatic agents in plastics, they show good film-forming property, hence good conductivity and good adhesion to the substrates.
(e) In JP-A-60229904 (JP-B-05017923), there are described examples in which a product of quaternization of an aminoalkyl acrylate is used as an antistatic functional group. In the examples, a cationic copolymer obtained by quaternizing an ethylene-ethyl acrylate-dimethylaminoethyl acrylate terpolymer with a trialkyl phosphate is blended with a polyolefin resin, polyester elastomer, polystyrene resin, ABS resin, polyamide resin and the like to give an antistatic resin composition.
(f) In JP-A-06179716, there are disclosed, by the present inventors, ethylene-acrylic acid-acrylate ester-acryloylaminoalkyltrialkylammonium copolymers and a method for their production. These cation-modified copolymers contain not only acrylate ester units but also positively introduced carboxylic acid units and, as a result, have the advantages detailed below.
The carboxylic acid units and amide structure units form intermolecular ionic bonds to thereby apparently increase the molecular weight of such a cation-modified copolymer. As a result, the viscosity, from melt kneading the copolymer becomes comparable to that of a thermoplastic resin to be molded and the copolymer is finely dispersed in the resin to provide a high level of antistatic effect at low addition levels. Furthermore, owing to the formation of ionic bonds as mentioned above, the resin internally supplemented with the cation-modified copolymer acquires improved shock resistance and flexibility.
(g) In JP-A-04292638, there is described a method of producing antistatic coatings which comprises using a cationic acrylate as an antistatic function group, and applying to a substrate the cationic acrylate and a polymerizable compound which contains at least two acryloyloxy and/or methacryloyloxy groups, together with an acryloyl derivative having alkylene oxide groups as side chains, followed by crosslinking for curing. The method uses, as the cationic acrylate, a product of quaternization of an aminoalkyl acrylate with a sulfate or sulfonate ester.
(h) In JP-A-06073210, there is described a method of obtaining antistatic coatings which comprises applying a mixture of a polyfunctional acrylate and an amino-containing acrylate to a substrate, then photocuring the coating using a photopolymerization initiator and treating, with heating, the cured coating with an alkyl sulfate ester or sulfonate ester for quaternary ammonium salt formation. There are disclosed, by way of example, certain resin films and resin sheets thus rendered antistatic.
(i) In JP-A-05032808, it is stated that synthetic resin moldings with durable and high-level antistatic property can be obtained by applying a partial quaternization reaction product derived from an amino-containing alkoxysilane and an alkyl sulfate ester or sulfonate ester and that the moldings are effectively applicable in manufacturing photomagnetic disks and the like.
The prior art cation-modified polyolefins mentioned above, however, when incorporated, in the practical use thereof, into polyolefins, styrenic resins, ABS resins, polymethyl methacrylate (P-MMA) resins, polyesters, polyamides, polycarbonates and like thermoplastic resins to give antistatic polymer alloys, for instance, pose the problems outlined below.
The use of the cation-modified polyolefins mentioned above under (a) and (b) in film production results in deteriorated transparency of the films because of poor compatibility. Mechanical characteristics, typically shock resistance, are also markedly decreased. The cation-modified polyolefins mentioned above under (c) and (d) are indeed improved versions with respect to compatibility but are not satisfactory with respect to shock resistance and other mechanical characteristics.
In the above-mentioned case (e), the trialkyl phosphate to be used for quaternization is expensive and renders the antistatic resins economically disadvantageous. In addition, the quaternization reaction generally fails to proceed quantitatively and, as a result, there remain unreacted tertiary amino groups, namely dimethylaminoethyl acrylate units. The use of a cation copolymer containing the remaining dimethyl-aminoethyl acrylate units as a resin composition component results not only in inferior antistatic property but also in discoloration supposedly due to denaturation of the remaining amino groups in the step of processing under heating or, when said copolymer is incorporated in thermoplastic resins containing amide or ester bonds, such as polyamide resins and polyester resins, marked decreases in mechanical strength characteristics tend to result.
On the other hand, in the above-mentioned cases (d) and (f), the extent of discoloration during processing under heating is less as compared with the case (e) mentioned above, hence the cationic copolymer can be suitably used. However, with this copolymer, one cannot yet satisfactorily cope with the raised processing temperature required for resin processing at increased speeds.
When the above-mentioned prior art cation-modified polyolefins are used in aqueous dispersion form, the following problems are encountered. Thus, the cation-modified polyolefins mentioned above under (a) and (b) are inferior in conductivity, and the cation-modified polyolefins mentioned above under (c) and (d) have indeed improved conductivity but are still unsatisfactory in adhesion to plastic, glass, paper and other substrate surfaces.
The coating-type antistatic agents described in the publications cited above under (g), (h) and (i) are cured on the substrate surface to acquire a crosslinked structure, hence impro frictional resistance and adhesion to substrate surfaces. However, the curing of them may often be insufficient under certain curing conditions. If the curing is insufficient, stickiness of the substrate surface, namely the so-called tack, will result and the substrate, when piled one on top of the other up, may possibly become inseparable from one another. Furthermore, since the antistatic agents are to be subjected to coating and curing, the range of applications thereof is naturally limited and the agents cannot yield thermoplastic resin compositions.
In the publication cited above under (e), mention is made, by way of example, of an antistatic paper sheet or polyester film obtained by coating the paper sheet or film with an aqueous dispersion of the cationic copolymer mentioned above. In that case, however, economic disadvantages cannot yet be overcome.
For economically improved production of films, trimmings resulting from film cutting are generally melted by heating for recycling. Accordingly, even coating-type antistatic agents are required to be heat-resistant. In such a case, the aqueous dispersions mentioned above under (c), (d) and (f) are quite incompetent, while the antistatic agents mentioned above under (g), (h) and (i), which are heat-curable, cannot be used for recycling at all.